1. Field of the Invention
The present invention relates to scanning probe microscopy, and, more particularly, to providing means for automatically replacing probe tip assemblies within a scanning probe microscope without requiring manual intervention by the operator.
2. Background Information
In a scanning probe microscope, a scanning movement is established between a surface of a sample being investigated and a very sharp, very small probe tip. The phrase "scanning probe microscope" is meant herein to describe a device in which the scanning movement is derived from movement of the sample, from movement of the probe tip, or from a combination of these two types of movement, with movement of the sample being used to move between points at which measurements are made, while the scanning movement occurring within the probe itself is used to make measurements in the vicinity of each such point. This phrase is also meant to include an important group of devices known as "atomic force microscopes."
The probe tip of a scanning probe microscope is typically mounted to a distal end of a cantilever, the proximal end of which is attached to an excitation actuator. The excitation actuator is a piezoelectric actuator driven to cause the cantilever, and thereby the probe, to vibrate vertically. The excitation actuator itself is additionally moved vertically by means of a Z-axis actuator, which is typically driven in response to changes in the amplitude of vibration of the probe tip. Changes in amplitude of vibration are caused by variations in the height of the sample surface, which change the level of engagement between the probe tip and the sample. The Z-axis actuator is driven, for example, to maintain the amplitude of vibrations at a constant level, with the level of the signal driving the Z-axis actuator being recorded to provide an indication of the height of the sample surface.
As the scanning probe microscope moves from being a tool of basic research to more widespread use in the inspection of manufactured parts having critical surfaces, a number of limitations of the device and difficulties with its use become apparent. In particular, the probe tips themselves, being small and sharp, and being subject to high levels of stress, tend wear out or break quickly. A probe tip is typically changed as a probe assembly including the cantilever and the excitation actuator. Since such assemblies are particularly small and fragile, they are subject to handling damage whenever they are changed. Furthermore, the electrical connections to the excitation actuator present additional difficulties when a probe assembly has to be replaced. Also, since a scanning probe microscope used is an inspection tool is ideally operated almost continuously, the time required to change probes manually can have a significant effect on the throughput achieved in an inspection station.
Furthermore, since there is a variety of types of tips for a scanning probe microscope, with individual types of tips being customized for different modes of measurement, there is typically a need to switch types to take different types of measurements, even on the same sample. In many applications of scanning probe microscopy, probe tips are changed more often because of a need to introduce n different type of tip than because tips become worn out or broken.
Therefore, what is needed is a method for facilitating the process of changing the probe assemblies. In particular, such a method should allow such assemblies to be changed without manual intervention by the operator.